I am stumped... it's frustrating when you see a problem as going to be easy to solve and it turns out to be real challenge.

All I want to do is use a difference key as a revealing mask on another video and then composit that over another video... i have spent two days on this... I have no idea why it is not working!

here is an example of what i want to do, and how i think it sould work, it works ok but am sure there is an easier way.

swap-alpha-channels-with-jit-unpack-jit-pack

On Aug 14, 2006, at 8:09 PM, Timothy Devine wrote:

> I am stumped... it's frustrating when you see a problem as going to 

> be easy to solve and it turns out to be real challenge.

> All I want to do is use a difference key as a revealing mask on 

> another video and then composit that over another video... i have 

> spent two days on this... I have no idea why it is not working!

> here is an example of what i want to do, and how i think it sould 

> work, it works ok but am sure there is an easier way.

You need to explain better what exactly you want to do and what apect 

of your patch is not working for you. Your patch seems to work as 

expected by your patch design as far as I can tell. I'm not sure why 

you're subtracting the red difference key from the chilis.jpg, but I 

assume you have a reason for that. I'm also not sure why you're 

alphablending with colorwheel and then trying to do a luminance key 

to it. However, perhaps this is just for illustration and there would 

otherwise be a fourth stream for the luminance key. Hard to say.

Otherwise your patch seems simple and an appropriate way to achieve 

what I believe you're describing. I've attached a version of a 

difference keying example I use when teaching at bottom. It only 

makes a binary mask, but is otherwise similar to what you are doing 

You could speed things up a bit if you use 1 plane matrices for your 

lowpass filter, and the absdiff operator, replacing jit.brcosa with 

jit.charmap or jit.map. Alternately, you could make much faster using 

the GPU, but that will be more involved. Once you get it working on 

the CPU, you might then look at porting your algorithm to a single 

>
> I am stumped... it's frustrating when you see a problem as going to  
> be easy to solve and it turns out to be real challenge.
>
> All I want to do is use a difference key as a revealing mask on  
> another video and then composit that over another video... i have  
> spent two days on this... I have no idea why it is not working!
>
> here is an example of what i want to do, and how i think it sould  
> work, it works ok but am sure there is an easier way.

You need to explain better what exactly you want to do and what apect  
of your patch is not working for you. Your patch seems to work as  
expected by your patch design as far as I can tell. I'm not sure why  
you're subtracting the red difference key from the chilis.jpg, but I  
assume you have a reason for that. I'm also not sure why you're  
alphablending with colorwheel and then trying to do a luminance key  
to it. However, perhaps this is just for illustration and there would  
otherwise be a fourth stream for the luminance key. Hard to say.

Otherwise your patch seems simple and an appropriate way to achieve  
what I believe you're describing. I've attached a version of a  
difference keying example I use when teaching at bottom. It only  
makes a binary mask, but is otherwise similar to what you are doing  
prior to the luminance key.

You could speed things up a bit if you use 1 plane matrices for your  
lowpass filter, and the absdiff operator, replacing jit.brcosa with  
jit.charmap or jit.map. Alternately, you could make much faster using  
the GPU, but that will be more involved. Once you get it working on  
the CPU, you might then look at porting your algorithm to a single  
shader for the GPU.

here is an updated version that shows you what i want to do. I took your advice with the GPU stuff ... i think i get it, it works much faster!

If you are using Jitter 1.6, you should have a look at the 

cc.alphaglue.jxs shader with param lum2alpha 1. This will take the 

luminance of the second input and use that as the alpha channel for the 

left input. You will then need an alphablend shader, which I have so 

kindly offered below. Save the following text as co.alphablend.jxs and 

throw it in your jitter-shaders/composite folder.

Hi Timothy,
If you are using Jitter 1.6, you should have a look at the 
cc.alphaglue.jxs shader with param lum2alpha 1.  This will take the 
luminance of the second input and use that as the alpha channel for the 
left input.  You will then need an alphablend shader, which I have so 
kindly offered below.  Save the following text as co.alphablend.jxs and 
throw it in your jitter-shaders/composite folder.

It seems like the right way to go. My only problem is the Erase from the trigger object erases my absdiff slab, so I can't create a mask. also i am not sure if the alphablending composite operator was all that was supposed to be in the text file that i created and copied into my jitter-shaders/composite folder. the shader I created does not detect it.

I will keep trying with the alphablending composite operator, do not really understand it fully. my patch is below.

It seems like the right way to go.  My only problem is the Erase from the trigger object erases my absdiff slab, so I can't create a mask.  also i am not sure if the  alphablending composite operator was all that was supposed to be in the text file that i created and copied into my jitter-shaders/composite folder.  the shader I created does not detect it.

Is there an alphablending composite operator already in max? I can't seem to find one. Is there any other way to combine two images, one with an alpha in openGL using a slab, like jit.alphablend?

Is there an alphablending composite operator already in max?  I can't seem to find one.  Is there any other way to combine two images, one with an alpha in openGL using a slab, like jit.alphablend?


There are any number of ways to combine 2 images in opengl. You could

use 2 layered jit.gl.videoplanes. Another way would be to use a

compositing slab operation and display the result on a single

jit.gl.videoplane. Look in your jitter-shaders/composite folder, all

of the photoshop layer blend modes are there. Have a look at tutorial

> Is there an alphablending composite operator already in max? I can't seem to find one. Is there any other way to combine two images, one with an alpha in openGL using a slab, like jit.alphablend?

There are any number of ways to combine 2 images in opengl.  You could
use 2 layered jit.gl.videoplanes.  Another way would be to use a
compositing slab operation and display the result on a single
jit.gl.videoplane.  Look in your jitter-shaders/composite folder, all
of the photoshop layer blend modes are there.  Have a look at tutorial
42 for more information.

On 8/17/06, Timothy Devine  wrote:
>
> Hi all,
>
> Is there an alphablending composite operator already in max?  I can't seem to find one.  Is there any other way to combine two images, one with an alpha in openGL using a slab, like jit.alphablend?
>
>
>
>
>


If i use 2 layered jit.gl.videoplanes will that utilize the alpha channel if it is there? The Photoshop blend modes won't use the alpha.

If i use 2 layered jit.gl.videoplanes will that utilize the alpha channel if it is there?  The Photoshop blend modes won't use the alpha.

> If i use 2 layered jit.gl.videoplanes will that utilize the alpha channel if it is there?

Yes depending on your blend_mode attribute.

The Photoshop blend modes won't use the alpha.

True, but you can modify them to use the alpha channel however you

want. It's quite easy to do. If you don't know GLSL, there are a

number of tutorials online that can exaplin the basics. Personally, I

would go this route as it's more flexible than using the OpenGL fixed

On 8/17/06, Timothy Devine  wrote:
>
> If i use 2 layered jit.gl.videoplanes will that utilize the alpha channel if it is there?

True, but you can modify them to use the alpha channel however you
want.  It's quite easy to do.  If you don't know GLSL, there are a
number of tutorials online that can exaplin the basics.  Personally, I
would go this route as it's more flexible than using the OpenGL fixed
function pipeline's blend_modes.

FWIW, Andrew Benson just posted an alphablend shader to the list earlier

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mail2web - Check your email from the web at

FWIW, Andrew Benson just posted an alphablend shader to the list earlier
this week. Check the archives...

--------------------------------------------------------------------
mail2web - Check your email from the web at
http://mail2web.com/ .


Actually, here is a question ive been meaning to ask, for the OpenGL 

blend modes, do any of them have 'photoshop' equivalents? for example 

6, 1 seems like overlay. The reason I ask, is so I can give the modes 

some accurate names in a UI in building, rather than just numbers.

I did a rudementary search, to no avail. Far too much signal to noise.

On Aug 17, 2006, at 10:30 PM, jkc@musork.com wrote:

> FWIW, Andrew Benson just posted an alphablend shader to the list 

> --------------------------------------------------------------------

> mail2web - Check your email from the web at

Actually, here is a question ive been meaning to ask, for the OpenGL  
blend modes, do any of them have 'photoshop' equivalents? for example  
6, 1 seems like overlay. The reason I ask, is so I can give the modes  
some accurate names in a UI in building, rather than just numbers.

>
> FWIW, Andrew Benson just posted an alphablend shader to the list  
> earlier
> this week. Check the archives...
>
> -Joshua
>
> --------------------------------------------------------------------
> mail2web - Check your email from the web at
> http://mail2web.com/ .
>
>
>

FWIW, I just emailed the shader directly to Timothy, but putting 

together an alphablend shader would make a great first project for 

learning GLSL. It's amazing what you can accomplish with just a couple 

FWIW, I just emailed the shader directly to Timothy, but putting 
together an alphablend shader would make a great first project for 
learning GLSL.  It's amazing what you can accomplish with just a couple 
lines of code.

Sorry, I can't seem to find the shader. Could someone link me to it?

Could you send me this interesting shader please? (co.alphablend.jxs)

It could be very nice because it misses some parts directly in the post. Can you send it in an attachment to avoid the missing parts?

Could you send me this interesting shader please? (co.alphablend.jxs)
It could be very nice because it misses some parts directly in the post. Can you send it in an attachment to avoid the missing parts?

swap alpha channels with jit.unpack jit.pack